Gas Chromatography-mass Spectrometry Instrument Research Articles

Determination of polycyclic aromatic hydrocarbons in olive oil by a completely automated headspace technique coupled to gas chromatography‐mass spectrometry

A new and completely automated method for the determination of ten relevant polycyclic aromatic hydrocarbons (PAHs) in olive oil is proposed using an extraction by the headspace (HS) technique. Quantification and confirmation steps are carried out by gas chromatography-mass spectrometry (GC-MS) combining simultaneously selected-ion monitoring (SIM) and tandem mass spectrometry (MS/MS). This combination offers on one hand an increased sensitivity and on the other hand, selective and reliable qualitative information. Sample pretreatment or clean-up are not necessary because the olive oil sample is put directly into an HS vial, automatically processed by HS and introduced into the GC-MS instrument for analysis. Because of its high selectivity and sensitivity, a triple-quadrupole (QqQ) detector coupled with the gas chromatograph allows us to limit handling. Each sample is completely processed in approximately 63 min (45 min for HS isolation and 18 min for GC-MS determination), a reduced time compared with previously published methods. The chemical and instrumental variables were preliminarily optimized using uncontaminated olive oil samples spiked with 25 microg kg(-1) of each target compound. The final method was validated to ensure the quality of the results. The precision was satisfactory, with relative standard deviation (RSD) values in the range 3-9%. Recovery rates ranged from 96 to 99%. Limits of detection (LOD) were calculated as 0.02-0.06 microg kg(-1) and the limits of quantification (LOQ) were obtained as 0.07-0.26 microg kg(-1). It must be mentioned that the LOD and LOQ are much lower than the maximum levels established by the European Union (EU) in oils and fats intended for direct human consumption or for use as an ingredient in foods, which are set at 2 microg kg(-1). All the figures of merit are completely in accordance with the latest EU legislation. This fact makes it possible to consider the proposed method as a useful tool for the control of PAHs in olive oils.

Urine Steroid Profile of Judo Competitors Affected by Acute Physical Exercises

A heterogeneous group of 10 male and 15 female judo players are utilized in this study. The subjects complete a standardized maximal treadmill exercise test. Urine samples are collected at the pre- and postexercise stages. The urine steroids are measured using a gas chromatography-mass spectrometry instrument. In rest and after exercise, significantly higher testosterone and epitestosterone concentrations in males (p < 0.01) are found. The etiocholanolone-dehydroepiandrosterone (DHEA) ratio is significantly lower in males than females (p < 0.05). In both males and females, etiocholanolone concentration significantly decreases with the effect of exercise (p < 0.05). 11-OH etiocholanolone concentration also significantly decreases, but only in females (p < 0.05). Positive correlation is found between the changes of the etiocholanolone and epitestosterone concentration caused by exercise.

Large-volume injection gas chromatography-mass spectrometry for automated broad-spectrum drug screening in horse urine.

A rapid, sensitive, and rugged method for detecting drugs and drug metabolites in extracts of horse urine is described. The use of large-volume injection (LVI) gas chromatography-mass spectrometry (GC-MS) for analysis of horse urine extracts allowed automation of the derivatization procedure and reduction of the sample volume from 5 mL to 1 mL of urine. An autosampler and temperature-programmable inlet were used to automatically dissolve the sample extract and form trimethylsilyl derivatives of over 200 analytes. The suitability of this procedure for routine GC-MS detection of approximately 80 basic analytes in extracts of racehorse urine was investigated. The formation of derivatives using LVI with in-liner derivatization was compared to a manual procedure involving the dissolution of sample extracts in N,O-bis(trimethylsily)trifluoroacetamide, heating the resulting mixture, and injecting 1 or 2 microL of the mixture through a splitless injector into the GC-MS instrument. In all cases, the in-liner derivatization reactions were found to be as complete as conventional heating block procedures. Ruggedness testing of the method demonstrated that peak resolution, shape, and area were maintained through 40 consecutive injections of sample extracts. No evidence of the accumulation of interfering substances was observed. The limits of detection using LVI GC-MS for routine screening of basic drugs in urine were generally in the range of 5-25 ng/mL. The method is currently being used to detect basic analytes in horse urine extracts with a throughput of approximately 50 urine sample extracts per instrument per day.

Interconversion of 6- and 7-substituted tetrahydropterins via enzyme-generated 4a-hydroxytetrahydropterin intermediates

Publisher Summary This chapter discusses interconversion of 6- and 7-substituted tetrahydropterins via enzyme-generated 4a-hydroxytetrahydropterin intermediates. The 6R-tetrahydrobiopterin (BH 4 ) is the natural cofactor for phenylalanine, tyrosine, and tryptophan hydroxylase, as well as nitric oxide synthase. The usual method of identification and quantitation of BH 4 involves the use of reversed-phase high-performance liquid chromatography (HPLC) after oxidation to convert reduced pterins to their fully oxidized, fluorescent forms. Separation of 6- and 7-biopterin can be achieved by reversed-phase HPLC. However, the identification of chromatographic peaks on the basis of elution times of standards is not sufficient, especially when working with biological samples. Additional methods must be employed to confirm both identification and quantitation. The standard method involves the use of mass spectrometry. While gas chromatography-mass spectrometry instrumentation is not readily available in most laboratories, other convenient analytical methods can be used to identify and quantitate the mixtures of 6- and 7-biopterin. As described in the chapter, these include two dimensional HPLC, oxidation of pterin side chains with permanganate followed by separation of the pterin carboxylic acids, and periodateborohydride treatment to cleave the polyhydroxy side chains to corresponding hydroxymethylpterins, which can then be separated by HPLC.

Implementation of liquid secondary ion mass spectrometry on quadrupole mass spectrometers: Strategy, optimization, and evaluation

A detailed strategy for adding liquid secondary ion mass spectrometry (L-SIMS, similar to fast atom bombardment (FAB)) capability to a quadrupole mass spectrometer equipped with only electron ionization (EI) and chemical ionization (CI) sources is delineated. The complexity of modifications is held to a level whereby any moderately equipped machine shop could complete the work. The manufacturing of specific items to enable the reversible conversion of a Hewlett-Packard HP5985A EI/CI gas chromatography-mass spectrometry instrument to perform L-SIMS was kept to a minimum. The essential fabricated items consist of a source block, a lens assembly, and a sample probe. The rationale behind the construction, and the optimization of the size and placement of each part are described in detail. The new capabilities for L-SIMS experiments are demonstrated for selected biomolecules. Sensitivity evaluations demonstrate that protonated molecules of N 6-methyladenosine can be readily detected from as little as two picomoles of analyte.

Complex mixture analysis based on gas chromatography-mass spectrometry with time array detection using a beam deflection time-of-flight mass spectrometer

A beam deflection time-of-flight mass spectrometer was developed in conjunction with an integrating transient recorder to provide time array detection, permitting high mass spectral scan file acquisition rates for complex mixture analysis by capillary gas chromatography-mass spectrometry (GC-MS). Results are presented for the analysis of a urinary organic acid mixture by GC-MS at a scan file acquisition rate of 10 scan files per second (sf/s), showing the advantages of such data collection in the deconvolution of partially resolved components. The reconstructed total ion current (RTIC) chromatogram available from data acquired at this scan file generation rate is shown to be comparable to the profile obtained from a flame ionization detector in representing the chromatography performed under identical experimental parameters. The RTIC chromatogram available from the database obtained at 10 sf/s is compared with that available from a database obtained at 1 sf/s, the latter representing that scan rate typically used with most GC-MS instruments. The advantages of the higher scan file acquisition rate in representing the chromatographic profile and in allowing mass spectral data to be obtained for components in the complex mixture that are unresolved chromatographically are discussed.

Gas chromatographic-mass spectrometric analysis of endogenous levels of estradiol in plasma and in cytosol from rat uterus

A method that permits the analysis of low levels of estradiol in plasma from women, men and rats and in cytosolic fractions of uterine tissue is described. The samples are extracted with Amberlite XAD-2 and a phenolic fraction is isolated on a lipophilic ion exchanger. Less polar contaminants in this fraction are separated from estradiol on Sephadex LH-20. Estradiol from human plasma can then be analysed by gas chromatography-mass spectrometry (GC-MS) as the trimethylsilyl ether using a capillary column and single ion monitoring of m/z 416. Samples from rat plasma and uterine cytosol require final purification by high-performance liquid chromatography prior to the GC-MS analysis. The approximate detection limits with the GC-MS instrument used were 1 – 10 −11-2 – 10 −11 moles/l in plasma and 5 – 10 −11 moles/kg in the uterus. Problems in the purification procedures and the specificity and sensitivity of GC-MS analyses are discussed.

Review of pollutants in petroleum refinery wastewaters and effect upon aquatic organisms

In the past decade, the number of organic chemical contaminants identified in oil refinery wastewaters has risen from less than 20 to over 300. This increase in knowledge was made possible by advances in gas chromatography-mass spectrometry instrumentation and new techniques to maximize resolution of capillary chromatography. The types of compounds identified in refinery wastewaters are similar to those identified in crude oils; i.e., aliphatic, aromatic, alkyl aromatic, polynuclear aromatic hydrocarbons, and some hydrocarbons containing nitrogen, sulfur, and oxygen. The contaminants in oil refinery wastewaters acutely lethal to aquatic organisms can be removed by biological treatment systems. However, biological treatment systems may not be capable of removing all deleterious contaminants. Long-term fathead minnow bioassays of biologically treated refinery wastewaters resulted in 10%–50% mortality after 14–16 days of exposure. The lethal effects were eliminated by sequential treatment with dual media filtration-activated carbon adsorption.

Variance analysis of error in selected ion monitoring assays using various internal standards. A practical study case.

This study contains a practical application of variance analysis for the evaluation of precision in selected ion monitoring using stable isotope variants or chemically related compounds as internal standards. Variance analysis is applied to determine the relative contributions of the errors due to long-term and short-term effects of instrument stability. The technique allows the resolution of variance due to sample manipulation from that introduced by the gas chromatography mass spectrometry instrumentation. This provides an objective measure of potential internal standards. Evaluation of the dependency of these errors upon concentration indicates appropriate weighing factors to be applied for regression analysis.